Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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1. Which of the following statement is correct?

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

(B) The increase in air movement increases the evaporation from the human body.

(D) Both (A) and (B)

2. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

0.2

1.2

3. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Equally

Unpredictable

Less

4. Rating of a domestic refrigerator is of the order of

40 tons

5 tons

10 tons

0.1 ton

5. Cooling water is required for following equipment in ammonia absorption plant

Evaporator

Absorber

Condenser

Condenser, absorber and separator (rectifier)

6. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Involves no change in volume

Takes place at constant pressure

Takes place at constant temperature

Takes place at constant entropy

7. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

None of these

Super-cooling

Sub-cooling or under-cooling

Normal cooling

8. Which of the following is not a desirable property of a refrigerant?

Large latent heat

Good electrical conductor

High risibility with oil

Low boiling point

9. A bootstrap air cooling system has

Four heat exchangers

One heat exchanger

Three heat exchangers

Two heat exchangers

10. The domestic refrigerator uses following type of compressor

Piston type reciprocating

Axial

Miniature sealed unit

Centrifugal

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11. In a refrigeration system, heat absorbed in comparison to heat rejected is

Less

Same

More for small capacity and less for high capacity

12. For obtaining high COP, the pressure range of compressor should be

Optimum

Any value

Low

High

13. The vapour compression refrigerator employs the following cycle

Rankine

Reversed Carnot

Carnot

Reversed Rankine

14. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

15. The operating pressure for refrigerating units using R-12 as a refrigerant is

15 bar

2 bar

8 bar

30 bar

16. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Carbon dioxide

Freon

Ammonia

Brine

17. The freezing point of sulphur dioxide is

-135.8°C

-77.7°C

-56.6°C

-75.2°C

18. Freon group of refrigerants are

Non-inflammable and toxic

Toxic

Inflammable

Nontoxic and non-inflammable

19. Critical temperature is the temperature above which

A gas will never liquefy

Water will evaporate

A gas will immediately liquefy

Water will never evaporate

20. In a refrigeration system, the expansion device is connected between the

Evaporator and compressor

Receiver and evaporator

Condenser and receiver

Compressor and condenser

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21. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(D) Difference of (A) and (B)

(B) Heat stored in the human body

(A) Heat dissipated to the surroundings

22. Which of the following cycles uses air as the refrigerant?

Bell Coleman

Carnot

Stirling

Ericson

23. The minimum temperature to which water can be cooled in a cooling tower is

Dew point temperature of air

Ambient air temperature

Dry bulb temperature of air

Wet bulb temperature of air

24. The capillary tube, as an expansion device, is used in

Water coolers

All of these

Room air conditioners

Domestic refrigerators

25. Highest temperature encountered in refrigeration cycle should be

Above critical temperature

Near critical temperature of refrigerant

At critical Temperature

Much below critical temperature

26. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

2.15

1.25

5.12

27. Most thermostatic expansion valves are set for a superheat of

5°C

20°C

15°C

10°C

28. The bank of tubes at the back of domestic refrigerator is

Capillary tubes

Evaporator tubes

Refrigerant cooling tubes

Condenser tubes

29. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

(T₁ - T₂)/T₁

(T₂ - T₁)/T₁

T₂/ (T₂ - T₁)

T₁ / (T₂ - T₁)

30. The boiling point of ammonia is

-77.7°C

-33.3°C

-30°C

-10.5°C

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31. In a lithium bromide absorption refrigeration system

None of these

Water is used as a refrigerant and lithium bromide as an absorbent

Ammonia is used as a refrigerant and lithium bromide as an absorbent

Lithium bromide is used as a refrigerant and water as an absorbent

32. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

1: 9

9: 1

1: 1

1: 3

33. The curved lines on a psychrometric chart indicates

Dry bulb temperature

Dew point temperature

Relative humidity

Wet bulb temperature

34. The condition of refrigerant after passing through the condenser in a vapour compression system is

Dry saturated vapour

Wet vapour

Saturated liquid

Superheated vapour

35. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

None of these

Positive

Negative

Zero

36. The value of C.O.P in vapour compression cycle is usually

Always less than unity

Any one of the above

Always more than unity

Equal to unity

37. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.6

0.376

0.4

0.67

38. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

1.33

4.33

3.33

2.33

39. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Collect vapours

Detect liquid in vapour

Collect liquid refrigerant and prevent it from going to compressor

Superheat the vapour

40. A thermostatic expansion valve in a refrigeration system

Is suitable only for constant load systems

Maintains different temperatures in evaporator in proportion to load

None of the above

Ensures the evaporator completely filled with refrigerant of the load

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A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

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